The present invention relates to a two-dimensional image detecting device which can detect an image of radiation such as an X-ray, a visible radiation, or an infrared radiation, and further concerns a manufacturing method thereof.
Conventionally, a two-dimensional image detecting device for radiation has been known in which semiconductor sensors for detecting an X-ray by generating electrical charge (electron-hole pair) are two-dimensionally disposed in a matrix form, each sensor is provided with an electrical switch, and the electrical switches are successively turned on for each line and electrical charge of the sensors is read for each raw. A specific structure and principle of such a two-dimensional image detecting device are described in xe2x80x9cD. L. Lee, et al., xe2x80x98A New Digital Detector for Projection Radiographyxe2x80x99, SPIE, 2432, pp. 237-249, 1995xe2x80x9d, xe2x80x9cL. S. Jeromin, et al., xe2x80x98Application of a-Si Active-Matrix Technology in a X-ray Detector Panelxe2x80x99, SID 97 DIGEST, pp. 91-94, 1997xe2x80x9d, and Japanese Laid-Open Patent Publication No.342098/1994 (Tokukaihei 6-342098).
Referring to FIGS. 11 and 12, the following explanation describes the specific structure and principle of the conventional two-dimensional image detecting device for radiation.
FIG. 11 is a schematic diagram showing the conventional construction of the two-dimensional image detecting device for radiation. Further, FIG. 12 is a schematic diagram showing a sectional structure for one pixel of the two-dimensional image detecting device for radiation.
As shown in FIGS. 11 and 12, the two-dimensional image detecting device for radiation is provided with an active-matrix substrate having electrode wires (gate electrode 52 and source electrode 53) in an XY matrix form, a thin film transistor (TFT) 54 and a storage capacitor (Cs) 55, on a glass substrate 51. Moreover, a photoconductive film 56, a dielectric layer 57, and an upper electrode 58 are formed on virtually the entire surface of the active-matrix substrate.
The storage capacitor 55 has a construction in which a Cs electrode 59 is opposed via an insulating film 61 to a pixel electrode 60 connected with a drain electrode of the thin-film transistor 54.
For photoconductive film 56, a semiconductive material is used to generate electrical charge (electron-hole pair) by exposure to radiation such as an X-ray. According to the aforementioned literatures, amorphous selenium (a-Se), which has high dark resistance and favorable photoconductivity, has been used for the photoconductive film 56. The photoconductive film (a-Se) 56 is formed with a thickness of 300xcx9c600 xcexcm by using a vacuum evaporation method.
Further, an active-matrix substrate, which is formed in a manufacturing process of a liquid crystal display device, can be applied to the aforementioned active-matrix substrate. For example, the active-matrix substrate used for an active matrix liquid crystal display device (AMLCD) is provided with the TFT made of amorphous silicon (a-Si) or polysilicon (p-Si), an XY matrix electrode, and a storage capacitor. Therefore, only a few changes in arrangement make it easy to use the active-matrix substrate as that of the two-dimensional image detecting device for radiation.
The following explanation describes a principle of operations of the two-dimensional image detecting device for radiation having the above-mentioned structure.
Electrical charge (electron-hole pair) is generated in the photoconductive film 56 when the photoconductive film 56 such as an a-Se film is exposed to radiation. As shown FIGS. 11 and 12, in the two-dimensional image detecting device, the photoconductive film 56 and the storage capacitors (Cs) 55 are electrically connected in series with each other; thus, when voltage is applied between the upper electrode 58 and the Cs electrode 59 in the two-dimensional image detecting device for radiation, electrical charge (electron-hole pair) generated in the photoconductive film 56 moves to a positive electrode side and a negative electrode side. As a result, the storage capacitors (Cs) 55 stores electrical charge. Further, an electron blocking layer 62 made of a thin insulating layer is formed between the photoconductive film 56 and the storage capacitor (Cs) 55. The electron blocking layer 62 acts as a blocking photodiode for preventing electrical charge from being injected from one side.
With the above-mentioned effect, the thin-film transistor (TFT) 54 comes into an open state in response to input signals of gate electrodes G1, G2, G3, . . . , and Gn so that the electrical charge stored in the storage capacitors (Cs) 55 can be applied to the outside from source electrodes S1, S2, S3, . . . , and Sn. The electrode wires (gate electrodes 52 and source electrodes 53), the thin-film transistor (TFT) 54, and the storage capacitors (Cs) 55, etc. are made in a matrix form; therefore, it is possible to obtain two-dimensional image information of an X-ray by line sequentially scanning signals inputted to gate electrodes G1, G2, G3, . . . , and Gn.
Additionally, in the case when the photoconductive film 56 has photoconductivity for a visible radiation and an infrared radiation as well as for the radiation such as an X-ray, the above-mentioned two-dimensional image detecting device for radiation acts as a two-dimensional image detecting device for detecting the visible radiation and the infrared radiation.
However, the conventional two-dimensional detecting device for radiation has used a-Se as the photoconductive film 56. Since the a-Se has dispersive conductivity of photoelectric current, that is peculiar to amorphous materials, the a-Se is inferior in response. The a-Se does not have sufficient sensitivity (S/N ratio) to an X-ray. Therefore, the conventional two-dimensional detecting device for radiation has a drawback as follow: the storage capacitor (Cs) 55 needs to be exposed to the X-ray for a long time to be fully charged, before reading information.
Further, in order to prevent electrical charge from being stored in the storage capacitor due to leakage current upon irradiation of X-ray, and in order to reduce leakage current (dark current) and to provide a protection against high voltage, the dielectric layer 57 is provided between the photoconductive film (a-Se) 56 and the upper electrode 58. However, it is necessary to add a sequence for removing electrical charge remained in the dielectric layer 57 for each frame; thus, the above-mentioned two-dimensional image detecting device can be used only when photographing a static picture.
In response to this problem, in order to obtain image data corresponding to a moving image, it is necessary to use the photoconductive film 56 instead of the a-Se. The photoconductive film 56 is made of a crystal (or polycrystal) material and a material being superior in X-ray sensitivity (S/N ratio). If the sensitivity of the photoconductive film 56 improves, it becomes possible to sufficiently charge the storage capacitor (Cs) 55 even when X-ray is applied for a short time, and high voltage does not need to be applied to the photoconductive film 56; thus, the dielectric layer 57 is not necessary.
As photoconductive materials which are superior in X-ray sensitivity, CdTe and CdZnTe have been known. Generally, photoelectricity absorption for X-ray proportionally increases to the fifth power of the effective atomic number of absorbed substance. For example, if it is assumed that the atomic number of Se is 34 and the effective atomic number of CdTe is 50, the sensitivity is expected to improve by approximately 6.9 times. However, in the case when CdTe or CdZnTe is adopted instead of a-Se as a material of the photoconductive film 56 of the two-dimensional image detecting device for radiation, the following problem arises:
In the case of the conventional a-Se, a vacuum evaporation method can be adopted as a film-forming method and a film can be formed at a normal temperature; thus, it has been easy to form a film on the active-matrix substrate. Meanwhile, in the case of CdTe and CdZnTe, film-forming methods such as an MBE (molecular beam epitaxial) method and an MOCVD (metal organic chemical vapor deposition) method have been known. Especially in view of forming a film on a large substrate, it is understood that the MOCVD method is appropriate.
However, in the case when a material selected from CdTe and CdZnTe is made into a film by using the MOCVD method, the heat decomposition temperature of organic cadmium is approximately 300xc2x0 C. (dimethyl cadmium (DMCd)), and the respective heat deposition temperatures of organic tellurium is approximately 400xc2x0 C. (diethyl tellurium (DETe)) or 350xc2x0 C. (diisopropyl tellurium (DiPTe)); therefore, a high temperature of approximately 400xc2x0 C. is required for forming a film.
Generally, in the thin-film transistor (TFT) 54 which is formed on the active-matrix substrate, an a-Si film or a p-Si film is used as a semiconductive layer. The a-Si film and a p-Si film are formed at a film-forming temperature of 300-350xc2x0 C. while hydrogen (H2) being added, in order to improve the semiconductive property. The TFT element formed in such a process has a heat-resistance temperature of approximately 300xc2x0 C. If the TFT element is processed at a temperature exceeding the heat-resistance temperature, hydrogen is released from the a-Si film and the p-Si film; consequently, the conductive property is degraded.
Therefore, in view of the film-forming temperature, it has been practically difficult to make a material selected from CdTe and CdZnTe into a film on the active-matrix substrate by using the MOCVD method.
In order to solve the above-mentioned problem, as described in a specification and claims of a U.S. patent application Ser. No. 09/239,855 made by an inventor et al. of the present application, the inventor et al. of the present application are devising a method for separately forming an active-matrix substrate and an opposing substrate and for bonding the substrates via a bonding material.
As the bonding material for bonding the substrates, it is desirable to adopt a material which electrically and physically connects pixel electrodes on the active-matrix substrate and a photoconductive layer on the opposing substrate, and which maintains insulation between the adjacent pixel electrodes. Specifically, it is possible to adopt an anisotropic material in which conductive particles are dispersed in an insulating resin, and a conductive material which can be selectively placed merely on the pixel electrodes by patterning and electrodeposition.
As the above-mentioned anisotropic material, a material has been conventionally known, in which conductive particles are dispersed into an adhesive (binder). The available conductive particles include a metal particle such as Ni, a metal particle such as Ni that is plated with Au, a carbon particle, a metal-film coated plastic particle obtained by plating a plastic particle with Au/Ni, a transparent conductive particle such as ITO (Indium Tin Oxide), and a conductive particle composite plastic obtained by mixing a Ni particle into polyurethane. Moreover, as the adhesive, it is possible to adopt adhesives such as a thermosetting adhesive, a thermoplastic adhesive, and a photo-curing adhesive.
Further, as the conductive material which can be selectively disposed merely on the pixel electrodes, it is possible to adopt a photosensitive resin in which conductive particles and powders are dispersed, a conductive polymer which can be electrodepositted, and others.
In order to separately form the active-matrix substrate and the opposing substrate and to bond them, in the case of any one of the above materials, it is necessary to perform a thermocompression bonding on the entire substrates by using a pressing device, upon bonding the substrates. In this case, it is important to evenly press and heat the entire substrates.
As a method for pressing these substrates (pressing method), a pressing method using a rigid body has been known; however, this method is not so appropriate for bonding large substrates for the following reason. Upon bonding large substrates, it is necessary to apply an extremely large pressure on the entire substrates. For instance, when 40 cmxc3x9750 cm substrates are bonded to each other, on the assumption that a material used for bonding the substrates requires a pressure of 10 kgf/cm2, the entire substrates require a pressure of 20000 kgf. Therefore, a large pressing device is necessary. Further, the larger the substrates are, the more difficult it is to evenly press the entire substrates.
Meanwhile, a vacuum pressing method reduces a pressure (vaccum) of a gap between a pair of substrates which are bonded to each other, so that the substrates are pressed by using external atmospheric pressure. This method is superior in evenness of pressure; however, a space is necessary upon reducing a pressure (vaccum) between the substrates. Thus, this method cannot be adopted when the substrates are bonded to each other entirely via an anisotropic conductive material. This is because no space exists between the substrates. Further, this method is a pressing method using atmospheric pressure, so that it is not possible to obtain a pressure exceeding an atmospheric pressure.
The present invention is devised to solve the above-mentioned problems. The object is to provide a two-dimensional image detecting device in which the active-matrix substrate and the opposing substrate are connected to each other with high reliability, and a manufacturing method for the two-dimensional image detecting device that can connect the active-matrix substrate and the opposing substrate with high reliability.
In order to achieve the above-mentioned object, the two-dimensional image detecting device of the present invention, which has an active-matrix substrate including a plurality of electrode wires being disposed in a lattice form so as to intersect at a plurality of intersections, a plurality of switching elements respectively disposed at the intersections, and a plurality of pixel electrodes connected to the electrode wires via the switching elements; and an opposing substrate including electrode sections and a semiconductive layer having photoconductivity between the electrode sections and the pixel electrodes, is characterized in that the active-matrix substrate and the opposing substrate are disposed such that the pixel electrodes and the semiconductive layer oppose each other, the pixel electrodes and the semiconductive layer are bonded to each other and are electrically connected to each other via a conductive material, a sealing means is further provided at an edge of a connecting surface of either the active-matrix substrate or the opposing substrate for shutting off a space between the active-matrix substrate and the opposing substrate from the outside.
As with the invention of the U.S. application Ser. No. 09/239,855, the above arrangement makes it possible to separately form the active-matrix substrate and the opposing substrate and to form the semiconductive layer on the opposing substrate at a temperature higher than a heat resistance temperature of the switching elements on the active-matrix substrate. Therefore, a semiconductive material such and CdTe and CdZnTe, which has not conventionally been available due to a limit of a film-forming temperature, can be adopted for the semiconductive layer.
Moreover, with this arrangement, the space between the active-matrix substrate and the opposing substrate is sealed from the outside. Thus, when the outside of the active-matrix substrate and the opposing substrate, which are bonded to each other upon manufacturing the device, is allowed to enter a pressurized gas atmosphere by using an autoclave device, etc., it is possible to apply the same pressure as the outside pressure onto the entire substrates because of a pressure difference between the space and the outside. Consequently, the entire substrates can be evenly pressed. Hence, it is possible to provide the two-dimensional image detecting device in which the active-matrix substrate and the opposing substrate are connected to each other with high reliability.
Furthermore, according to this arrangement, the space between the bonding surfaces of the substrates is structurally sealed, so that an additional process is not necessary in a manufacturing process of the two-dimensional image detecting device.
Additionally, according to this arrangement, the sealing means is formed at an edge of the connecting surfaces of the substrates for shutting off the space between the substrates from the outside, so that it is also possible to protect the space between the bonding surfaces of the substrates and to improve the bonding strength.
In order to achieve the above object, a manufacturing method for the two-dimensional image detecting device of the present invention includes the steps of (a) forming the active-matrix substrate which has a plurality of the electrode wires being disposed in a lattice form so as to intersect at a plurality of the intersections, a plurality of the switching elements respectively disposed at the intersections, and a plurality of the pixel electrodes connected to the electrode wires via the switching elements, (b) forming the opposing substrate which has the electrode sections and the semiconductive layer having photoconductivity between the electrode sections and the pixel electrodes, (c) disposing the conductive material on either the pixel electrode side of the active-matrix substrate or the semiconductive layer side of the opposing substrate, (d) overlaying the active-matrix substrate and the opposing substrate onto each other such that the pixel electrode side of the active-matrix substrate and the semiconductive layer side of the opposing substrate oppose each other, and (e) bonding the overlaid active-matrix substrate and opposing substrate and connecting the substrates electrically via the conductive material, wherein the step (e) includes performing a heating operation while applying pressure to the substrates by using the autoclave device.
According to this method, it is possible to evenly press the entire substrates regardless of the size of the substrates upon bonding the active-matrix substrate and the opposing substrate, and a pressure for connecting the substrates can be readily adjusted in accordance with a kind of the conductive material. Further, a heating medium has a large density under a pressurized gas atmosphere, so that a heating rate increases in a heating operation, resulting in reduction in the manufacturing time. Therefore, it is possible to provide the manufacturing method for the two-dimensional image detecting device that can connect the active-matrix substrate and the opposing substrate with high reliability.
In order to achieve the above object, a manufacturing method for the two-dimensional image detecting device of the present invention includes the steps of (a) forming the active-matrix substrate which has a plurality of the electrode wires being disposed in a lattice form so as to intersect at a plurality of the intersections, a plurality of the switching elements respectively disposed at the intersections, and a plurality of the pixel electrodes connected to the electrode wires via the switching elements, (b) forming the opposing substrate which has the electrode sections and a semiconductive layer having photoconductivity between the electrode sections and the pixel electrodes, (c) disposing the conductive material on either the pixel electrode side of the active-matrix substrate or the semiconductive layer side of the opposing substrate, (d) overlaying the active-matrix substrate and the opposing substrate onto each other such that the pixel electrode side of the active-matrix substrate and the semiconductive layer side of the opposing substrate oppose each other, and (e) bonding the overlaid active-matrix substrate and opposing substrate and connecting the substrates electrically via the conductive material, wherein before step (e), step (g) is further included for sealing a surrounding part of the overlaid active-matrix substrate and opposing substrate so as to shutting off a space between the active-matrix substrate and the opposing substrate from the outside.
According to this method, in step (e), if the outside of the overlaid active-matrix substrate and opposing substrate is allowed to enter a pressurized gas atmosphere by using the autoclave device, etc., it is possible to evenly press the entire substrates regardless of the size of the substrates upon bonding the active-matrix substrate and the opposing substrate, and a pressure for connecting the substrates can be readily adjusted in accordance with a kind of the conductive material. Therefore, it is possible to provide the manufacturing method of the two-dimensional image detecting device that can connect the active-matrix substrate and the opposing substrate with high reliability.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.